1. Field of the Invention
The present invention relates to a composition for forming a silicon-containing film used in a multilayer resist process used for a microfabrication in a process for producing semiconductor devices, a silicon-containing film-formed substrate and a patterning process by use thereof.
2. Description of the Related Art
With high integration and speeding up of LSI, miniaturization of pattern sizes has progressed rapidly. Lithography technology has accomplished the formation of fine patterns in response to this miniaturization by shortening a wavelength of a light source and appropriately selecting a resist composition corresponding thereto. A positive resist composition used in a monolayer has been a basis thereof. In this monolayer positive photoresist composition, an exposed portion is dissolved to form the pattern by giving a skeleton possessing etching resistance to dry etching with chlorine-based or fluorine-based gas plasma to a resist resin and giving a resist mechanism to dissolve the exposed potion, and the processing substrate onto which the resist composition has been applied is dry-etched using a remaining resist pattern as an etching mask.
However, when a photoresist film to be used is directly miniaturized with keeping a film thickness, i.e., a pattern width is further reduced, a resolution performance of the photoresist film is diminished. When the pattern of the photoresist film is developed by a developer, a so-called aspect ratio is excessively increased. As a result, a pattern collapse occurs. Thus, with the miniaturization, the photoresist film thickness has been thinned.
Meanwhile, for processing the processing substrate, a method for processing the processing substrate by the dry etching using the photoresist film in which the pattern has been formed as the etching mask is typically employed, but actually no dry etching method capable of taking a perfect etching selectivity between the photoresist film and the processing substrate is available. Thus, the resist film is damaged during processing the processing substrate; the resist film collapses, and the resist pattern can not be precisely transferred to the processing substrate. Accordingly, with the miniaturization of: the pattern, higher dry etching resistance has been required for the resist composition.
Due to shortening the wavelength in an exposure wavelength, the resin having small light-absorption in the exposure wavelength is required for the resin used for the resist composition. Thus, for the change from i-beam to KrF and ArF, the resins have also changed from novolak resins to polyhydroxystyrene and the resins having an aliphatic polycyclic skeleton. However, actually an etching speed in the above dry etching condition has already become fast, and the recent photoresist composition having the high resolution tends to rather reduce the etching resistance.
From this, the processing substrate must be processed by dry etching using the photoresist film which is thinner and less etching resistant. It is an urgent need to assure materials and processes in this processing process.
As one of the methods for solving such problems, a multilayer resist process is available. In this method, a resist intermediate film whose etching selectivity is different from that of the photoresist film, i.e., a resist upper layer film is disposed between the resist upper layer film and the processing substrate, the pattern is obtained in the resist upper layer, subsequently the pattern is transferred onto the resist intermediate film by dry etching using the resulting pattern in the resist upper layer as the dry etching mask, and further the pattern is transferred onto the processing substrate by the dry etching using the resulting pattern in the intermediate film as the dry etching mask.
In a bilayer resist method which is one of the multilayer resist processes, for example, silicon-containing resin is used for the resist upper layer composition, and the novolak resin is used as the resist intermediate film (e.g., Japanese Patent Laid-Open (kokai) No. H6-95385). The silicon-containing resin exhibits the good etching resistance to the reactive dry etching with oxygen plasma, but is easily removed by the etching when fluorine-based gas plasma is used. Meanwhile, the novolak resin is easily removed by the etching in the reactive dry etching with the oxygen plasma, but exhibits the good etching resistance to the dry etching with the fluorine-based gas plasma and the chloride-based gas plasma. Thus, a novolak resin film is formed as the resist intermediate film on the processing substrate, and a resist upper layer film using the silicon-containing resin is formed thereon. Subsequently, the pattern is formed in the silicon-containing resin film by post treatments such as exposure to energy beam and development. Using this as the dry etching mask, the portion of the novolak resin where the resist pattern has been removed is removed by the reactive dry etching with the oxygen plasma to transfer the pattern in the novolak film. Using this pattern transferred to the novolak resin as the dry etching mask, the pattern can be transferred to the processing substrate using the etching with the fluorine-based gas plasma or the chloride-based gas plasma.
In such a pattern transfer by the dry etching, when the etching resistance of the etching mask is sufficient, the transferred pattern having a relatively good shape is obtained. Thus, a pattern collapse caused by friction by a developer upon resist development hardly occurs, and the pattern having a relatively high aspect ratio can be obtained. Therefore, for example, when the resist film using the novolak resin has the thickness corresponding to the film thickness of the intermediate film, even in the fine pattern which could not be formed directly because of the pattern collapse upon development due to the aspect ratio, according to the above bilayer resist method, the novolak resin pattern having the sufficient thickness as the dry etching mask for the processing substrate is obtained.
Furthermore, as the multilayer resist process, a trilayer resist method which can be performed using the common resist composition used in the monolayer resist method is available. For example, an organic film by novolak and the like is formed as the resist lower layer film on the processing substrate, the silicon-containing film is formed as the resist intermediate film thereon, and an ordinary organic photoresist film is formed as the resist upper layer film thereon. The organic photoresist film exhibits the better etching resistance than the silicon-containing resist intermediate film in the dry etching with the fluorine-based gas plasma. Thus, the resist pattern is transferred to the silicon-containing film as the resist intermediate film using the dry etching with the fluorine-based gas plasma. According to this method, even when the resist composition in which it is difficult to form the pattern having the sufficient film thickness for directly processing the processing substrate or the resist composition having the insufficient dry etching resistance to process the substrate is used, if the pattern can be transferred to the silicon-containing film, like the bilayer resist method, it is possible to obtain the pattern of the organic film having the dry etching resistance enough to be processed.
As the silicon-containing resist intermediate film used in the above trilayer resist method, silicon-containing inorganic films by CVD such as SiO2 films (e.g., Japanese Patent Laid-Open (kokai) No. H7-183194) and SiON films (e.g., Japanese Patent Laid-Open (kokai) No. H7-181688); SOG (spin on glass) (e.g., Japanese Patent Laid-Open (kokai) No. H5-291208, J. Appl. Polym. Sci., Vol. 88, 636-640 (2003)) and crosslinking silsesquioxane films (e.g., Japanese translation of PCT international application No. 2005-520354) as the films obtained by spin coating are used, and polysilane films (e.g., Japanese Patent Laid-Open (kokai) No. H11-60735) is also believed to be used. Among them, the SiO2 films and the SiON films have the high performance as the dry etching mask when the organic film as the resist lower layer film is dry-etched, but a particular apparatus is required for forming the film. On the contrary, the SOG films, crosslinkable silsesquioxane films and the polysilane films can be formed by the spin coating and heating and are believed to have a high process efficiency.
An application range of the multilayer resist process is not limited to an attempt to enhance a resolution limit of the resist film. As a via first method which is one of the methods for processing the substrate, when a processing intermediate substrate has a large bump, if the pattern is formed by a single resist film, the resist film thickness has a large difference. Thus, the focus can not be adjusted precisely upon resist exposure. In such a case, the bump is buried with a sacrificial layer to flatten, then the resist film is formed thereon and the resist pattern is formed. In this case, the multilayer resist process is inevitably employed (e.g., Japanese Patent Laid-Open (kokai) No. 2004-349572).
There are several problems in the silicon-containing film conventionally used in such a multilayer resist process. For example, when the resist pattern is formed by photolithography, it is well-known that exposure light is reflected on the substrate and interferes with incident light to cause a so-called stationary wave. In order to obtain the fine pattern having no edge roughness in the photoresist film, it is necessary to insert an antireflection film. In particular, reflection control is an essential condition in a state-of-the-art high NA exposure condition.
Thus, for controlling the reflection, it is necessary to insert an organic antireflection film between the photoresist film formed on the silicon-containing film and silicon-containing film in the multilayer resist process, particularly in the process in which the silicon-containing film is formed as the resist intermediate film by CVD. However, when the organic antireflection film is inserted, it becomes necessary to form the pattern in the organic antireflection film using the photoresist film as the dry etching mask. Upon dry etching, the organic antireflection film is processed by dry etching using the photoresist film as the mask, and subsequently the silicon-containing film is processed. Thus, a load of the dry etching for processing the organic antireflection film is added to the upper layer photoresist film. In particular, the film thickness is thinned in the-state-of-the-art photoresist film, and this dry etching load can not be missed out. Thus, the trilayer resist method in which a light absorbable silicon-containing film which generates no etching load as the above is applied as the resist intermediate film has been noticed.
As such a light absorbable silicon-containing film utilized as the resist intermediate film, the light absorbable silicon-containing film of a spin coating type is known. For example, a technique for giving an aromatic structure as a light absorbable structure has been disclosed (Japanese Patent Laid-Open (kokai) No. 2005-15779).
However, an aromatic ring structure which absorbs the light efficiently acts to reduce the dry etching speed in the dry etching processing with the fluorine-based gas plasma, and thus is disadvantageous for the dry etching of the resist intermediate film without adding the load to the photoresist film. Thus, it is not preferable to add such a light absorbable substituent in a large amount, and it is necessary to minimize the amount of introduction thereof.
Furthermore, the dry etching speed in the reactive dry etching with the oxygen gas plasma generally used when the resist lower layer film is processed using the resist intermediate film as the dry etching mask is preferably smaller for enhancing an etching selection ratio of the resist intermediate film and the resist lower layer film. In order to obtain such a dry etching property, the resist intermediate film in which a content of silicon having the high reactivity to fluorine-based etching gas is high as possible is desired. As described above, it can be said that the film containing the high content of silicon having the high reactivity to fluorine-based gas is preferable as a requirement from processing conditions of the upper layer photoresist film and the lower layer organic film.
In an actual composition for forming the silicon-containing intermediate film of the spin coating type, an organic substituent is contained so that a silicon-containing compound can be dissolved in an organic solvent. In the lithography using KrF excimer laser, among the conventionally known silicon-containing films as the resist intermediate films, the composition which forms the SOG film has been disclosed in J. Appl. Polym. Sci., Vol. 88, 636-640 (2003).
However, since there is no description for the light absorbable group in this composition, it is predicted that there is no antireflection function in the silicon-containing film obtained from this composition.
Thus, there is a possibility that the highly fine resist pattern can not be obtained because the reflection upon exposure can not be avoided in the lithography using a state-of-the-art high NA exposing machine.
As described above, the good dry etching property and realization of the highly fine resist pattern profile between the resist upper layer film and the resist lower layer film are required for the silicon-containing film as the resist intermediate film used in the multilayer resist process. A storage stability of the composition for forming the silicon-containing compound is particularly problematic in the composition for forming the silicon-containing film for forming the intermediate film containing the high content of silicon. In the composition for forming the silicon-containing film, silanol groups present in the silicon-containing compound in the composition are condensed to change a molecular weight of the composition for forming the silicon-containing film in some cases.
Generally when water is allowed to act upon a hydrolyzable silicon compound (monomer) in the presence of an acid catalyst, a hydrolyzable substituent bound to a silicon atom undergoes the hydrolysis to form a silanol group. This silanol group is condensed with another silanol group or an unreacted hydrolyzable group to form a siloxane bond. And this reaction is continuously repeated to form a so-called oligomer, polymer and in some cases a silicon-containing compound referred to as sol. At that time, the silanol groups derived from the monomers, oligomers and polymers produced by the hydrolytic reaction in the system are condensed sequentially from the most reactive one, the silanol groups in the monomer, the oligomer and the polymer are consumed and the silicon-containing compound is formed. This condensation reaction progresses endlessly and sometimes progresses until a silicon-containing compound solution is finally gelled. In such a case, change of the film thickness and change of lithography performance are observed. In particular since the change of the lithography performance is sensitive, even though the increase of the film thickness and the change of a molecular weight by condensing the silanol groups in the molecule are not observed, the change of the highly fine pattern shape is observed.
Conventionally, it has been described in C. J. Brinker and G. W. Scherer, “Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing”, Academic Press, San Diego (1990) that when such a highly reactive silanol group is kept in an acidic state, the compound can be relatively stabilized. Furthermore, adding the water to enhance the storage stability has been disclosed in J. Appl. Polym. Sci., Vol. 88, 636-640 (2003) and Japanese Patent Laid-Open (kokai) No. 2004-157469 and Japanese Patent Laid-Open (kokai) No. 2004-191386.
However, the silicon-containing compound in the composition for forming the silicon-containing film produced by the method described above, even though such a procedure is given, actually the condensation reaction of the silanol groups can not be stopped completely, the silicon-containing compound gradually changes with time, and nature of the silicon-containing film obtained from the changed composition for forming the silicon-containing film also changes. Thus, the compound must have been stored in a refrigerator or a freezer until just before the use, its temperature must have been backed to a use temperature (usually 23° C.) upon use, and the composition must have been used up promptly.
Furthermore, in the actual process for producing the semiconductor devices, there is the case where a failure occurs on an applied film formed on the substrate and the film must be reprocessed. The conventional SOG film has almost the same composition as in SiO2. Thus, dry delamination with hydrofluoric acid or fluorine-based gas is used for delaminating this film, but this delamination method largely damages the substrate.
For this problem, the composition for forming the silicon-containing film is required where a wet delamination using a sulfuric acid/hydrogen peroxide mixture or an ammonia/hydrogen peroxide mixture as generally used for the conventional process for producing the semiconductor devices can be performed.